Guide horn structure for endless track of high speed multi-terrain vehicles

ABSTRACT

This invention relates to endless tracks and systems used to propel track laying vehicles [i.e., vehicles which use endless tracks rather than tires to contact the terrain over which they are driven, e.g., tractors, tanks, bulldozers, etc.] and, more particularly, to an improved rubber track design and system allowing the endless track to be driven more efficiently at highway speeds. The track is made from a polymer adapted to travel over a drive sprocket, a plurality of guide wheels and a tensioning wheel, the track having a first exterior ground engaging surface and a second interior drive sprocket engaging surface, the track comprising: a carcass portion in which reinforcements are embedded into the polymer; a plurality of tread lugs disposed on the first engaging surface; a plurality of drive lugs disposed on the second engaging surface and a plurality of guide horns disposed on the second engaging surface.

RELATED APPLICATION DATA

This present patent application is a continuation-in-part of commonlyassigned U.S. patent application Ser. No. 09/984,307, filed on Oct. 29,2001 and entitled “Endless Track for High Speed Multi-Terrain Vehicles”,now U.S. Pat. No. 7,090,312, the content of which is incorporated hereinby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to endless tracks used to propel track layingvehicles [i.e., vehicles which use endless tracks rather than tires tocontact the terrain over which they are driven, e.g., tractors, tanks,bulldozers, etc.] and, more particularly, to an improved rubber trackdesign allowing the endless track to be driven more efficiently athighway speeds.

2. General Discussion

Numerous types of vehicles are frequently used in terrain in which it isdifficult for pneumatic tires to operate. Both military vehicles, suchas tanks and amphibious vehicles, and civilian vehicles, such astractors and recreational vehicles, are sometime utilized on terrainswhich are very soft, for example sand surfaces. Pneumatic tires are notcapable of efficient operation on such soft surfaces, as they tend toburrow into the surface, rather than riding across the surface.

Endless track vehicles have been developed for use on terrains in whichpneumatic tired vehicles are impractical. See for example U.S. Pat. No.3,361,488 (Ohm et al), U.S. Pat. No. 3,688,858 (Jespersen), U.S. Pat.No. 3,734,577 (Snellman) and U.S. Pat. No. 3,955,855 (Massieon et al).In many types of terrain these vehicles provide improved performancerelative to the performance of pneumatic tired vehicles; still,difficulties are encountered with existing endless track vehicles.

Originally, such tracks were made of a plurality of metal links or shoespivotally attached to each other to form an endless track which are veryheavy, cause serious damage to roads and other surfaces on which theyrun and result in an uncomfortable ride for the passengers. See forexample U.S. Pat. No. 2,823,082 (Bauer) and U.S. Pat. No. 4,530,546(Meisel, Jr.). Heavier vehicles still use metal tracks.

The above referenced conventional tracks have the disadvantages of beingnoisy and vibration prone, not sufficiently durable and/or not usable onroad surfaces. This is because of the conventional configurations anduse of metal parts. Accordingly, substantial efforts have been made toconstruct quieter, smoother operating and more durable tracks fortracked vehicles.

A need has developed for a form of vehicle appropriate for both normalhighway use and off road use over snow covered, very uneven, or muddyterrain. There is significant need for such a vehicle not only duringarmed conflicts but also following natural emergencies (snow and windstorms, floods, etc.), and such vehicles are at present particularlyneeded in developing countries. Unfortunately, almost all availableautomotive vehicles require infrastructure (paved highways, bridges,etc.) for practical operation, and the developing countries are decadesaway from having the necessary infrastructure for such conventionalvehicles. Further, most load carrying off road vehicles presently in usehave either very large wheels or very cumbersome tracks which are heavy,slow moving, and inappropriate for use on paved roads at normal highwayspeeds.

Rubber endless tracks have become popular due to an increase inconstruction in urban areas where vehicles having tracks must drive onthe pavement and because there is a demand for low soil compactionfarming. With the combination of rubber technology and a tremendousamount of trial and error, various types of rubber tracks are nowavailable in the industry. They are used on excavators, dump carriers,boring machines, combines, tractors, and the like See for example U.S.Pat. No. 5,279,378 (Graiwey & al) and U.S. Pat. No. 6,267,458 (Hansen etal). Most of them operate on the job site only and are transportedbetween sites by trucks or trailers. To eliminate the inconvenience oftransporting the vehicle between job sites, a vehicle which can operateboth on public roads at normal speeds and in off road constructionenvironments is required. However, such a vehicle will have to beconstructed so as to provide little damage to the pavement, include lessvibration and noise, and operate with less maintenance and lubrication.Furthermore, vibrations to be transmitted to occupants are mitigated andpaved roads are not significantly damaged.

A number of hybrid tracks have been proposed where the links or shoesare made of metal which is provided with a rubber cover or insert. Seefor example U.S. Pat. No. 2,359,586 (Sayler), U.S. Pat. No. 2,369,130(Benson), U.S. Pat. No. 2,409,502 (Leguillon et al), U.S. Pat. No.3,148,921 (Batur et al), U.S. Pat. No. 4,109,971 (Black et al), U.S.Pat. No. 4,359,248 (Kortering) and U.S. Pat. No. 4,588,233 (DenBesten).

3. Description of the Related Art

[NOTE: As used herein, the term “rubber” relates to any elastic andprimarily non metallic materials such as rubber, elastomers, or otherpolymers and/or combinations thereof used in the manufacture of endlesstracks].

Most rubber tracks are formed around a basic carcass or belt. Thecarcass includes an endless belt shaped rubber like elastic member, anumber of core bars (usually of metal) embedded therein and aligned inthe longitudinal direction thereof and extending in traverse directionsthereof, and steel cords (tension resistant members) embedded in theendless elastic member to surround the core bars circumferentiallyoutwardly. See for example U.S. Pat. No. 4,904,030 (Ono), U.S. Pat. No.5,295,741 (Togashi et al), U.S. Pat. No. 5,511,869 (Edwards et al) andU.S. Pat. No. 6,241,327 (Gleasman).

Some have suggested the construction of endless rubber tracks using aplurality of interconnected polymeric modules. See for example U.S. Pat.No. 4,861,120 (Edwards et al) U.S. Pat. No. 5,005,922 (Edwards et al).

Terrain contacting lugs are formed integral with the exterior surface ofthis basic belt element. Known rubber tracks include large lugs having avariety of well known orientations, e.g., formed generally perpendicularto the track axis, or at an angle to the track axis, or in a chevron ormodified chevron design. These latter special tracks also includeinterior lugs or horns for maintaining the track in alignment as ittravels over the circumferences of the rubber tired wheels, such lugsbeing located either in the centre of the interior surface of the track(for designs appropriate for fitting between the tires of dual wheels)or in two aligned rows near the outside edges of the track (forreceiving a single tire there between). See for example U.S. Pat. No.5,447,365 (Muramatsu & al) and U.S. Pat. No. 5,540,489 (Muramatsu & al).

The tracks are carried by a plurality of rotating elements (wheels,sprockets, etc. . . . ) mounted on the track laying vehicle, the tracksbeing maintained in circumferential contact with these rotating elementsand being driven thereby (or, in the case of trailer-like non drivenvehicles, being supported for rotation thereon).

Problems encountered in actually reducing such an endless rubber trackto practice include how to maintain adequate tension on such belt, howto drive such tracks and keeping the belt in lateral alignment with thewheels when the wheels are subject to large lateral loads. Otherproblems are maintaining the structural integrity and providing longlife for the belt, mid rollers, drive wheels, and idler wheels.

While smaller rubber tracked vehicles are commercially available, thesedo not carry adequate loads for military vehicles (including tanks),normal multi passenger or produce transports, and their drive wheels caneasily become mired in heavy mud or snow.

As stated in U.S. Pat. No. 5,295,741 (Togashi et al), when a vehicleequipped with rubber tracks moves on sandy terrain or quarries, therubber tracks are likely to shift from advancing directions of thevehicle due to elongations and contractions of the rubber-like materialin vertical and horizontal and other directions. As a result, the rubbertracks unavoidably get off the sprocket wheels or track rollers of thevehicle. Various attempts have been made in order to prevent thedislodgement of the rubber tracks from the vehicle, but they have notmet with success.

Known rubber tracks, when mounted on the rotating wheels of vehicles,exert distinct resistive forces that must be overcome to move thevehicle, i.e., resistive forces in addition to those forces created bythe load being carried and/or generated by the terrain. These furtherresistive forces relate to the additional tensions required to stretchthe heavy lugs of the tracks around the wheels over which they aremounted and to the additional friction generated between the tracks andthe terrain. While the latter frictional resistive forces are a valuableattribute under wet or snowy conditions, they add undesirably to energycosts when driving the vehicle over flat, hard surfaces.

The aforementioned patents are representative of a large body of patentswhich purport to solve one or more of the rubber track systemimplementation problems. Such body of patents constitutes documentaryevidence that efforts to achieve this blend of track and wheelpropulsion systems have been exerted for over half a century withoutrealizing any practical measure of success. Solutions to the problems ofactually implementing a heavy-duty vehicular rubber track drive systemhave proven elusive and scientific scaling techniques have not, to date,been successfully applied to light duty vehicles for purposes ofdeveloping a heavy duty rubber track system. Thus, despite the long feltneed for and the advantages thereof, a heavy duty application vehicleutilizing such rubber track system is commercially unavailable today.

For this reason, most military tracked vehicles are still equipped withmetallic tracks. In an effort to reduce the inconveniences related tosuch metallic track systems, some tracks are provided with rubber padson the ground engaging side of the metallic track.

However, these metallic tracks still present significant inconveniencesin relation to wheeled vehicle. Some of these problems can be summarizedas follows:

Noise. The metallic track produces an excessively high level of noise.This fact can cause a significant strategic disadvantage when used inassociation with military vehicles since the enemy can detect thepresence of the military vehicle many miles away.

Damage. With respect to civilian vehicles equipped with such tracks ormilitary vehicles used in peace keeping missions, the metallic trackscan cause significant damage to the ground surface whether it be pavedor not.

Weight. Metallic tracks are very heavy. For example the typical weightof a metallic track used on an M113 tank is 1200 pounds while themetallic track used on a Bradley tank is 2500 pounds. Such a weight isboth an inconvenience with respect to the mobility of the vehicles andwith respect to their consumption of fuel.

Short lifespan. Metallic tracks have a short lifespan. Even metallictracks provided with rubber pads wear out extremely rapidly such thatthe pads need to be replaced every 500 to 1000 miles on a military tank.

Maintenance. Metallic tracks also require a lot of maintenance. Thereplacement of the rubber pads, the metallic links or shoes, etc.requires a continuous maintenance of the tracks.

Costs. Finally, the cost of manufacturing, maintenance and refurbishingare extremely high.

As seen above, efforts to develop a rubber alternative to metallictracks have been relatively successful in relation to “light” vehicles.However, such rubber tracks, although an improvement in many respectsover the known metallic tracks still have the following shortcomings inrelation to heavy equipment such as tanks:

De-tracking. De-tracking is a phenomenon by which a track loses contactwith the guiding system such that it will completely remove itself fromthe vehicle and thus cause it to stop. To limit this phenomenon, more orless rigid protuberances or guide horns are disposed along the interiorportion of the track to form a rampart which fits between guide wheels.These wheels are generally grouped in pairs and the space between thewheels allows the guide horns to past freely between them. Anotherelement which is important to reduce de-tracking is the use of anappropriate tension wheel.

Teeth Skipping. Tracks are powered by a motor mechanically connected toa sprocket which engages protuberances or drive lugs on the insidesurface of the track. If these drive lugs are allowed to skip over theteeth of the sprocket, damages to and premature wear of the track willoccur. The abrupt movements which result also cause significantdiscomfort to the passengers of the vehicle. In order to diminish suchteeth skipping phenomenon, the drive lugs on the track must produce assmall a friction as possible on the sprocket while allowing the sprocketto firmly engage the track. Again, tensioning of the track is a criticalelement.

Wear and tear. Tracks can also prematurely break down due to a number ofother internal and external elements such as: breakage of reinforcingrods, tearing of the reinforcing fabric, cables and fibres and theabrasion, piercing, tearing and de-lamination of the rubber components.

The prior art solutions which are adapted for regular industrial andagricultural vehicles are inadequate when faced with the severity of theproblems faced by military vehicles. Indeed, the high weight of militaryvehicles combined to the high speeds and strong accelerations (bothlateral and longitudinal) create high stresses in the track whichconsiderably amplify the aforesaid problems.

SUMMARY OF THE INVENTION

It is, thus, the objective of this invention to provide a workablesolution to the problems by taking into account that such vehicle'sundercarriage, to be truly useful, should be roadable, provide hightraction and low ground compression, and minimally disturb theunderlying terrain, as well as operate in the heavy duty working modeand provide a smooth ride for the operator in most soil conditions andtopography from level land to steep inclinations while performing usefulwork without breaking the belts, losing drive capability between engagedwheels and belts, or disengaging the belts from the wheels.

It is an object of the present invention to reduce such de-tracking,teeth skipping and wear and tear on all types of vehicles (military,industrial, agricultural and others).

It is another object of the present invention to replace metallic tracksby a reinforced rubber track which provides the advantages of metallictracks (including good traction, support and adaptability to all typesof terrain) while diminishing significantly the disadvantages (noise,damage to the ground surface, weight, short lifespan, maintenance andhigh costs).

There is therefore provided a track for use on a tracked vehicle madefrom a polymer adapted to travel over a drive sprocket, a plurality ofguide wheels and a tensioning wheel, the track having a first exteriorground engaging surface and a second interior drive sprocket engagingsurface, the track comprising:

-   -   a carcass portion in which reinforcing means are embedded into        the polymer;    -   a plurality of tread lugs disposed on the first engaging        surface;    -   a plurality of drive lugs disposed on the second engaging        surface;    -   a plurality of guide horns disposed on the second engaging        surface, each the guide horn having a forward surface, a rear        surface, a top surface and two lateral surfaces;

wherein the upper forward portion of each the lateral surface is beveledand the top surface tapers toward the front surface.

While the invention is applicable to endless tracks for all track layingvehicles, its particular purpose is to increase the efficiency of heavytrack laying all terrain vehicles such as military tanks that arespecifically designed for normal speed travel over paved highways aswell as for appropriate use over unpaved roads and uneven off roadterrain.

Other aspects and many of the attendant advantages will be more readilyappreciated as the same becomes better understood by reference to thefollowing detailed description and considered in connection with theaccompanying drawings in which like reference symbols designate likeelements throughout the figures.

The features of the present invention which are believed to be novel areset forth with particularity in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Accordingly it is intended that the foregoing disclosure and showingmade in the drawings shall be considered only as an illustration of theprinciple of the present invention.

FIG. 1 is an overall side view of a track system in accordance with theinvention.

FIG. 1A is a fragmentary and enlarged side view of the sprocket wheelregion of the track system shown in FIG. 1.

FIG. 1B is a fragmentary and enlarged side view of the tension wheelregion of the track system shown in FIG. 1.

FIG. 2 is a perspective top view of a portion of a track in accordancewith the invention.

FIG. 3 is a perspective bottom view of the track shown in FIG. 2.

FIG. 4 is a side view of the track shown in FIG. 2 taken generally alongline B-B as shown in FIG. 2.

FIG. 5 is a cross section of the track shown in FIGS. 2 and 3 takengenerally along line A-A as shown in FIG. 3.

FIG. 6 is a perspective view of a sprocket wheel use to power a track inaccordance with this invention.

FIG. 7 is a cross sectional view of the sprocket wheel shown in FIG. 6taken generally along line C-C as shown in FIG. 1.

FIG. 8 is a cross sectional view of the guide wheel taken generallyalong line D-D as shown in FIG. 1.

FIG. 9 is a perspective view of a tension wheel for use with a track inaccordance with the invention.

FIG. 10 is a cross section of the tension wheel shown in FIG. 9 takengenerally along line E-E as shown in FIG. 1.

FIG. 1 shows a general side view of a rubber track system in accordancewith this invention installed on a military vehicle 10. The track systemcomprises an endless reinforced rubber track 100, a sprocket wheel 20, atension wheel 30 and a plurality of guide wheels 40 which support thevehicle and guide the track 100. This system is coupled to appropriatedrive means (not shown) through an appropriate suspension system (notshown). A similar system is disposed on the other side of the vehicle10.

As shown in FIGS. 2 and 3, a track 100 is typically built around a beltlike carcass 150 made of reinforced rubber. As noted above, the term“rubber” relates to any appropriate elastic polymer. The track 100comprises an external surface 200 and an internal surface 300. As shownin FIG. 2, a plurality of traction lugs 210, 220 and 230 are disposed onthe exterior surface 200. These traction lugs or tread interact with thesurface on which the vehicle 10 is being displaced to ensure appropriatetraction of the vehicle. The traction lugs are made out of a sufficientquality of rubber to support the normal wear of the tread due toabrasion.

As shown in FIG. 3, the interior surface 300 of the track 100 comprises:

-   -   a plurality of guide horns or lugs 320 which are consecutively        located along the longitudinal center line of the interior        surface 300. These guide lugs or horns form a quasi continuous        rampart 321 (best shown in FIG. 1) which fits in the gorge 29        formed in the sprocket wheel 20 (see FIG. 7), gorge 39 formed        between the outer and inner wheel portions 32 and 34 of the        tension wheel 30 (see FIG. 10) and the opening 49 between the        wheels 41 and 42 which form the guide wheel 40 (see FIG. 8). The        mating of the guide horns with the gorges and/or openings 29, 39        and 49 allows the track to be guided during the movement of the        vehicle;    -   a plurality of protuberances 330 which are called traction lugs        are provided along each side of the track 100. These traction        lugs are designed to matingly engage with corresponding cavities        23 in the sprocket wheel 20. They thus ensure the transmission        of power from the motor (not shown) to the track 100; and    -   flat running surfaces 310 and 315 are provided on each side of        the guide horns 320. The support wheels 40 running on these        running surfaces support the weight of the vehicle 10.

As illustrated in FIGS. 3 and 4, the guide horns 320, the traction lugs330 and the exterior tread lugs 210, 220 and 230 are placed on the trackin such a way as to form successive segments each having an identicalpitch 130. The various section are separated by sections 110 of thecarcass 150 on which no lug, horn or other protuberance is located thusforming a hinge which will allow the track to wrap itself around thevarious wheels forming the track system of this invention. When used inrelation to a military tank such as an M113 tank, the pitch 130 ispreferably between two inches and six inches. However, for a givensprocket wheel diameter, it is preferable to reduce the pitch in orderto increase the number of drive lugs 330 which at any given time areengaged into the sprocket cavities 23. The minimum number of drive lugs330 which are in contact with cavities 23 at any given time should befour.

In order to optimise the interaction between the track and the othercomponents of the track system to reduce de-tracking, skipping of teethand wear and tear, it is preferable that each component be optimised asdescribed hereunder.

As illustrated in FIG. 1 and more particularly in FIG. 1A, when thetrack system is properly installed on vehicle 10, track 100 is disposedaround the sprocket wheel 20 such that the wrap angle 160 can vary fromone vehicle to the other but is usually comprised between 30 degrees and180 degrees.

The sprocket wheel 20 is rigidly coupled to the motor (not shown)through appropriate transmission means (also not shown). As depicted inFIG. 6, the sprocket wheel 20 comprises two wheel portions between whichthe gorge 29, mentioned earlier, is defined. The outer perimeter 21 ofeach sprocket wheel portion is facetted such as to define asubstantially polygonal perimeter when viewed from the side. Each facet22 of the outer perimeter 21 has a length or pitch 26 and furthercomprises one traction lug receiving cavity 23.

Because the principal purpose of this sprocket wheel 20 is to transmitpower from the motor to the track 100, it is important to ensure a firmengagement between the track traction lugs 330 and the correspondingcavities 23 in the sprocket wheel 20. Appropriate engagement is obtainedwhen the track does not slide sideways or skip teeth on this sprocketwheel 20. Proper engagement is itself dependant on a certain number ofprincipal factors which summarised below.

As depicted in FIG. 7, the lateral displacements of the track 100 on thesprocket wheel 20 are prevented by the presence of the guide horns 320which engage in the gorge 29 (which separates the sprocket wheel intoparts). However, it is preferable that the width of the gorge beslightly larger (but not too much) than the width of the guide horns.The recommended spacing 28 (best shown in FIG. 7) for a M113 tank isbetween 1/16″ and 3/32″.

The lateral displacements and longitudinal displacements (resulting inteeth skipping) of the track 100 are further prevented by the mating ofthe traction lugs 330 within the corresponding cavities 23 in thesprocket wheel 20. The quality of the mating itself depends on severalfactors.

First, the longitudinal tension in the track 100 must be great enough sothat the vertical component of the tension forces compensates for theforces which extend radially between the walls of cavities 23 and thoseof the traction lugs 330.

Second, these contact forces depend on the material which are used andof the geometric forms given to these surfaces.

Third, the maintenance of the quality of these surfaces depends on theconditions of operation, the elastic deformation and wear.

The wrap angle 160 formed by the belt when it is wrapped around thesprocket wheel 20 (see FIG. 1A) as well as the number of traction lugs330 engaged in the cavities 23 of the sprocket wheel 20 have asignificant impact on the lateral, tangential and vertical displacementsof the track l00.

It has been determined by trial and error that:

i. the sprocket wheel 20 should contain a minimum of twelve (12) andpreferably fifteen (15) cavities 23 on each part thereof;

ii. the number of traction lugs 330 engaged in the cavities 23 mustpreferably be equal or larger than four (4) to ensure a firm engagementand reduce the chances of teeth skipping;

iii. the shape and dimensions of the cavities 23 are in directrelationship to those of the drive lugs 330. We have found that it ispreferable that the pitch 130 of the track 100 be slightly smaller thanthe pitch 26 of the facets 22 of the outer perimeter 21 of the sprocketwheel 20. The difference should preferably be between 0% and 1% in orderto compensate for stretch during high efforts and wear during the usefullife of the track;

iv. the use of a polymeric material having a high mechanical resistanceand high resistance to abrasion is preferable. In this respect, UHMWpolyethylene is one of the preferred materials;

v. gorge 29 in this sprocket wheel 20 should preferably be “V”-shaped tofacilitate the installation of the track 100 on the vehicle 10; and

vi. as shown in FIGS. 3 and 4, the traction lugs 330 have an anteriorsurface 332 and a posterior surface 334 presenting a generally prismaticcontour. The actual cross section of these traction lugs is preferablyof the type described in U.S. Pat. No. 4,605,389 (Westhoff) which isincorporated herein by reference. The length of the tangent t used inthe traction equation x2(1+y2)=t2 is a function of the thickness 120 ofthe track 100, of the position of the neutral axis 140 and of the height335 of each traction lug 330. Such a profile procures an optimalinterface during the operation of the vehicle.

We have determined by experimentation that the traction lugs 330 shouldpreferably have the following characteristics:

i. as depicted in FIG. 5, the interior surface 336 should be slightlyinclined by a first angle α which is preferably superior to 3 degreesand by a second angle β which is preferably greater than the first angleα to prevent interference with the wheels 40;

ii. as depicted in FIG. 8, the spacing 47 between the wheels 40 and thetraction lugs 330 should be large enough (larger than spacing 45 betweenthe wheels 40 and the guide horns 320) so that the wheels effectivelyguide the track 100 through the guide horns 320 rather than using thetraction lugs 330;

iii. as depicted in FIG. 4, the top portion 337 of the traction lugs 330should preferably be truncated and rounded;

iv. as depicted in FIG. 4, the base of the traction lugs 330 should beas wide as possible;

v. as depicted. in FIG. 5, the exterior surface 338 of each traction lugcan be angled more than the interior surface 336.

As shown in FIG. 1, when the track system of the invention is installedon a vehicle 10, the guide wheels 40 which support the vehicle run onthe track 100 which is itself disposed on the ground surface. The numberof guide wheels 40 should be appropriate for the weight of the vehicle.Indeed, guide wheels 40 support the entire weight of the vehicle as wellas resist lateral efforts which may result from turning the vehicle orhitting various objects during the displacement of the vehicle.

As shown in FIG. 8, each guide wheel 40 is formed of two wheels 43 and44 each of which having a band of rubber (respectively 41 and 42)disposed on its outer perimeter. Each of these rubber bands 41 and 42contacts the flat surfaces 310 and 315 on the interior 300 of the belt100. Wheels 43 and 44 are separated from each other so as to form agorge 49 between them. This gorge is designed to be slightly larger thanthe width of the guide horns 320 so as to leave a slight gap 45 on eachside of the guide horn 320. A gap 47 is also defined between the outerportion of rubber bands 41 and 42 and the interior portion of guide lugs330. It is preferable that the gap 45 be limited to between 1/16 of aninch and 3/16 of an inch in the case of an M113 tank. This spacing iscritical as if it is too tight it will cause high friction with theresulting serious inconveniences. On the other hand, if it is too big,it will encourage de-tracking of the track 100 and will render thevehicle much more difficult to be driven in a straight line. In order toincrease resistance of the vehicle to de-tracking, it is necessary thatthe gap 47 as shown be greater than the gap 45.

Guide horns 320 are designed so as to maximise the guiding of the track100. To do so, side surfaces 322 and 324 must cover an area as large aspossible so that their interaction with guide wheels 40 will be suchthat it creates as close as possible to a continuous rampart betweenthem (see FIG. 1).

However, their length should not be such that it compromises therotation of the track 100 around the sprocket wheel 20 and the tensionwheel 30. Therefore, it is preferable that the guide horns 320 betapered towards their top surface 329 as shown in FIG. 3 (see also FIGS.4 and 5). It is also preferable to have the top of each side 322 and 324of the guide horns tapered in the longitudinal direction correspondingto the movement of the track 100 when the vehicle is moving forward. Asa result, the top surface 329 of the guide horn, when viewed from thetop (as shown in FIG. 3), defines a triangular surface itself defining acorner 325 on the side of the guide horn which corresponds to the normalmovement of the track 100. Without the bevels 326 and 328, the track 100could have a greater tendency to de-track when lateral forces areapplied to the track 100. Indeed, when small lateral forces are appliedto the track 100, the side surfaces 322 and 324 of the guide horns 320will be pushed against the interior of the wheels 40, thus creating aneffective rampart preventing the de-tracking of the track 100. However,when large lateral forces are applied to the track 100, the sidesurfaces 322 and 324 will still be pushed against the interior of thewheels 40 but the track may be so misaligned with the general directionof the vehicle and the wheels 40 that there is a greater opportunity forthe track 100 to de-track itself from the vehicle. The angular shape ofthe bevels 326 and 328 will tend to push back the track 100 in thegeneral direction of the vehicle, thus preventing the de-tracking of thetrack 100. The use of bevels 326 and 328 thus significantly lowers thisrisk of de-tracking without significantly diminishing the area ofsurfaces 322 and 324. The bevels 326 and 328 are thus means added to theguide horns 320 to prevent de-tracking of the track 100.

The height and length of the guide horns 320 depend on the configurationof vehicle 10. However, we have found that it is preferable that theratio between the height and the width be approximately two. In this wayrotation around the sprocket wheel and the tension wheel is adequatewithout compromising the protection against de-tracking.

It is also extremely important that the guide horns 320 be rigid. Ifnecessary, they should be reinforced with known means which may includefibers and rigid inserts.

As shown in FIG. 1 and more particularly in FIG. 1B, when the track 100is installed on vehicle 10, it is wrapped around tension wheel 30therefore forming a wrap angle 170 which should preferably be between 30degrees and 180 degrees. The tension wheel 30 is generally located atthe rear of the vehicle and allows to maintain the necessary tension inthe track 100 to ensure that the traction lugs 330 maintain an adequatemating relationship with the cavities 23 in sprocket wheel 20.

As depicted in FIG. 9 and more particularly in FIG. 10, the tensionwheel 30 generally comprises inner wheel portion 34 and outer wheelportion 32 between which a gorge 39 is defined. As mentioned above, thegorge 39 is configured to receive the guide horns 320 of the track 100.

The tension wheel 30 should be designed to reduce the wear and abrasionof the track. Therefore, at least its exterior portion should be made ofa relatively soft material such as rubber. In order for the tensionwheel not to damage the track 100 it is necessary that the track 100 beprovided with reinforcing means such as cables, fibers or fabric.

While a preferred embodiment of the invention has been described herein,it should be apparent to those skilled in the art that variations andmodifications are possible without departing from the spirit of thisinvention.

1. A track for use on a tracked vehicle made from a polymer adapted totravel over a sprocket wheel, a plurality of guide wheels and atensioning wheel, said track having a first exterior ground engagingsurface and a second interior sprocket wheel engaging surface, saidtrack comprising: a) a carcass portion in which reinforcing means areembedded into said polymer; b) a plurality of tread lugs disposed onsaid first engaging surface; c) a plurality of drive lugs disposed onsaid second engaging surface; d) a plurality of guide horns disposed onsaid second engaging surface, each said guide horn having a forwardsurface, a rear surface, a top surface and two lateral surfaces; whereinthe upper forward portion of each said lateral surface is bevelled andsaid top surface tapers toward said front surface.
 2. A track as claimedin claim 1, wherein said upper rear portion is not bevelled.
 3. A trackas claimed in claim 1, wherein said guide horns comprise reinforcingmeans.
 4. A track as claimed in claim 3, wherein said reinforcing meansare rigid inserts.
 5. A track as claimed in claim 3, wherein saidreinforcing means are fibres.
 6. A track as claimed in claim 1, whereinsaid guide horns have a height and width and wherein the ratio betweensaid height and said width is approximately two.
 7. A track for use on atracked vehicle made from a polymer adapted to travel over a sprocketwheel, a plurality of guide wheels and a tensioning wheel, said trackhaving a first exterior ground engaging surface and a second interiorsprocket wheel engaging surface, said track comprising: a) a carcassportion in which reinforcing means are embedded into said polymer; b) aplurality of tread lugs disposed on said first engaging surface; c) aplurality of drive lugs disposed on said second engaging surface; d) aplurality of guide horns disposed on said second engaging surface;wherein each said guide horn comprises de-tracking prevention means. 8.A track as claimed in claim 7, wherein each said guide horns furthercomprise reinforcing means.